This invention relates to a bit holder for a miner and has been devised particularly though not soley for mounting on the cutting drums of continuous mining machines.
Continuous mining machines commonly incorporate various types of rotating cutting drums on which are mounted a plurality of bits or picks pointing outwardly from the surface of the drum and arranged such that when the drum is rotated against a face (e.g. a coal face) the bits or picks strike the face and sever the minerals therefrom. The bits are fastened to the drum by way of a pick holder which is commonly in two parts, a mounting base normally welded to the surface of the drum and a bit holder secured to the mounting base by way of detachable means such as a transverse pin or a set screw. Many of the pick holders currently in use develop degrees of wear after a short period of time allowing the bit to move or wobble relative to the drum, reducing the cutting efficiency of the miner and causing further accelerated wear in the bit and the pick holder. Attempts have been made to overcome these problems by providing pick holders with widened "ears" to provide a broader mounting base for the bit and also by providing various different types of clamping devices which will enable the bits to be readily removed and replaced as they wear while yet providing a firm location of the bit holder in the mounting base. Those pick holders incorporating the wide ears have problems in that the ears wear in use and also absorb cutting power from the mining machine as they contact the coal face. This problem is particularly acute in pick holders mounted on the cutting drum at the edges of the drum where the pick holder is bent over at an angle in order to cut into the corners, or where they are located next to the core breaker on hard head mining machines.
It is a further problem with existing pick holders that frequent tightening of the mounting set screw is necessary in order to maintain the integrity of the mounting of the bit holder in the mounting base and neglect of the tightening procedure can result in a loose bit holder and rapidly accelerated wear.
Many existing pick holders are also of comparatively low profile and require to be mounted on pedestals welded to the cutting drum in order to achieve the desired height of the point of the bit above the drum surface.